1. Field of the Invention
The present invention relates to a rolling mill for metal foil, that is used for subjecting a sheet material to strip processing into a rolled material by supplying it between a pair of work rollers.
2. Description of the Prior Art
FIGS. 10(a) to 10(d) are schematic views each showing the arrangement of rollers of a conventionally known rolling mill.
The rolling mill shown in FIG. 10(a) [hereinafter referred to as the two-high rolling mill] has a fundamental structure and comprises a pair of upper and lower work rollers W.sub.1 between which a sheet material S to be rolled is supplied for rolling the sheet material.
The rolling mill shown in FIG. 10(b) [hereinafter referred to as the four-high rolling mill] comprises a pair of upper and lower work rollers W.sub.2 and a pair of backup rollers B.sub.2 for supporting the work rollers thereon. Since the backup rollers B.sub.2 of the four-high rolling mill reduce flexing of the work rollers W.sub.2, the work rollers W.sub.2 can be made smaller in diameter than those of the two-high rolling mill.
The rolling mill shown in FIG. 10(c) [hereinafter referred to as the six-high rolling mill] comprises a pair of upper and lower work rollers W.sub.3 and two pairs of forward and backward backup rollers B.sub.3 for supporting the work rollers thereon. The work rollers W.sub.3 can be made much smaller in diameter than those of the four-high rolling mill.
The rolling mill shown in FIG. 10(d) [hereinafter referred to as the twelve-high rolling mill] comprises a pair of upper and lower work rollers W.sub.4, two pairs of forward and backward intermediate rollers M.sub.4 for supporting the work rollers thereon, and two pairs of three reinforcing bearing rollers R.sub.4 for supporting the pair of intermediate rollers M.sub.4 thereon. Each reinforcing bearing roller R.sub.4 comprises a plurality of roller bearings RB arranged side by side. Owing to the structure having the work rollers W.sub.4 supported by the intermediate rollers M.sub.4 and reinforcing bearing rollers R.sub.4, the work rollers W.sub.4 can be made smallest in diameter.
The smaller the work roller diameter, from that shown in FIG. 10(a) to that shown in FIG. 10(d), the smaller the power required. This not only enables reduction of rolling mill size and lowering of manufacturing cost, but also becomes an important factor for making a sheet material S to be rolled thinner. This has been confirmed from the theoretical point of view and the viewpoint of actual results.
In the various kinds of rolling mills cited above, the thickness of a sheet material S after being rolled can be made smaller in proportion as the diameter of the work rollers becomes smaller. According to the twelve-high rolling mill, whose work rollers are smallest in diameter, it is possible to obtain a rolled product having a sheet thickness of about 50 to about 9 .mu.m if the width of the rolled product is not more than 600 mm.
Furthermore, according to the twelve-high rolling mill, since the plurality of roller bearings RB constituting each reinforcing bearing roller R.sub.4 are set to be independently movable in their diameter directions, the thickness of a sheet material S to be rolled can be easily controlled in its width direction by adjusting the diameter-direction movement of the roller bearings, resulting in advantages in quality of the rolled product.
Continuing pronounced advances in the field of electronic technology have led to increasing demand for further enhancement of the performance of rolled products obtained by the aforementioned rolling mills. Higher performance products are needed in connection with, for example, rolled foil of copper alloy indispensable to the realization of multilayered prints on printed circuit boards or a smaller thickness of printed circuit boards; miniaturization, larger capacity and longer service life of secondary battery products; and higher density and integration of semiconductor products. In such applications, a thickness of 9 to 3 .mu.m is required and from the standpoint of enhancing yield, a width exceeding 750 mm is necessary.
These requirements can conceivably be met by making the diameter of the work rollers W.sub.4 of the twelve-high rolling mill smaller by increasing the rigidity or number of the intermediate rollers and reinforcing bearing rollers.
However, this solution would considerably increase the weight or number of the rollers involved in the strip processing with the rolling mills and consequently increases the mechanical loss and the influence of inertial weight. As a result, it would become very difficult to precisely control driving of the rollers, leading to inferior products passed between the work rollers, that not only have lengthwise elongation, intermediate elongation, composite elongation and one-sided elongation, but also exhibit easy fracture. Therefore, this solution cannot be put into practical use. When a product is fractured, there is a possibility of the fractions marring the peripheral surfaces of the rollers when they pass between the rollers. The subsequent repair requires much time. That is to say, a material for a rolled product of self-supportable shape having a width of not more than 600 mm and a thickness of not less than about 50 to about 9 .mu.m can be rolled within the scope of conventional rolling mill technologies or an extension of such technologies. However, these same technologies are the main obstacle to production of rolled metal foil difficult to produce in self-supportable shape having a thickness of 9 to 3 .mu.m.
In view of the above, the inventors conceived a six-high rolling mill that would be inferior to the twelve-high rolling mill in suppression of work roller flexure, but superior thereto in accuracy of roller-drive control. They repeatedly carried out experiments, analyses and improvements as regards the limits of rolled metal foil production using the six-high rolling mill and consequently were able to obtain some uniform results. That is to say, they found that it was required to make the diameter of the work rollers smaller, accurately control driving of the rollers and guide both the material to be rolled and the rolled product in the immediate vicinity of the work rollers in order to produce rolled metal foil that is too thin and too wide to be self-supportable in shape. They actually confirmed that such an improved six-high rolling mill for metal foil could produce a rolled product thinner than the limits of rolled material production using the twelve-high rolling mill, though not reaching the aforementioned currently demanded level.
In the improved six-high rolling mill for metal foil, however, when the diameter of the work rollers in FIG. 11(a) is reduced to that of the work rollers in FIG. 11(b) (W.sub.3.fwdarw.W.sub.3 ') so that the demanded level can be attained, the problems listed below still remain due to restrictions on the arrangement of the work rollers W.sub.3 and backup rollers B.sub.3.
1 The interval r between the pair of backup rollers B.sub.3 opposed across a passing line for a material S to be rolled is reduced with decreasing work-roller diameter to that of the work rollers W.sub.3 ', so that there is a possibility of the backup rollers B.sub.3 coming into contact with each other. This means that reduction of the work roller diameter to that of the work rollers W.sub.3 ' reaches a limit.
2 Mutual approaching of the backup rollers B.sub.3 makes it difficult to secure spaces for disposing guides for the material S to be rolled and the rolled product in the immediate vicinity of the work rollers W.sub.3 '.
3 The interior angle .alpha. formed by connecting the axis a of a work roller W.sub.3 ' to the axes b of the contacting backup rollers B.sub.3 has to be set obtuse, and the reaction force of the roll load applied onto the backup rollers B.sub.3 is increased. This is disadvantageous in the aspect of controlling the roll load and leads to a possibility of the bearing portions for the backup rollers B.sub.3 being damaged in an early stage.
These problems can be solved to some extent by making the diameter of the backup rollers B.sub.3 smaller. However, since the backup rollers B.sub.3 are required to have desirable rigidity so that they can prevent the work rollers W.sub.3 ' from being flexed, they fail to fulfill their own functions when formed to a small diameter.
The main object of the present invention under these circumstances is to provide a rolling mill for metal foil that enables easy and precise production of even metal foil too thin and too wide to be self-supportable in shape.
To be specific, the object of the present invention is to provide a rolling mill for metal foil that can produce rolled metal foil of extremely small thickness and large width with spaces secured for disposing guides for a material to be rolled and a rolled product in the immediate vicinity of a pair of work rollers without reducing the diameter of backup rollers.
Another object of the present invention is to provide a rolling mill for metal foil, in which the interior angle formed by connecting the axis of a work roller to the axes of contacting backup rollers can be made acute and the roll load can be controlled with ease.